Various enhanced oil recovery techniques are known for increasing the production of heavy crude oil, including gas injection, chemical injection, microbial injection and thermal recovery. Thermal recovery methods involve the introduction of a heated fluid, such as steam, into an oil field in order to decrease the viscosity of the oil and thus to facilitate its removal.
U.S. Pat. No. 5,058,675 discloses a method and apparatus for the extraction of oil and gas from oil shale wherein solar-heated steam is injected into a well in an open system wherein there is no water recovery from the well. Such systems consume a large quantity of water and are not practical for all applications.
The recovery and reuse of water for a steam injection enhanced oil recovery system requires the removal of minerals from the recovered water prior to reuse as feed water for a boiler, since such minerals will concentrate in the boiler and cause an unacceptable scale buildup which inhibits heat transfer and necessitates periodic cleaning operations. U.S. Pat. No. 8,167,041 discloses a method for the recovery of hydrocarbon from oil sands which avoids such scaling problems. A solar thermal power plant is used to generate steam. The steam in injected via an injection well into a formation in the ground to extract bitumen at an oil producing well. FIG. 7 of that patent shows a solar heating system which has a first closed circuit of a heat transfer fluid. A heat exchange unit (steam generator) is provided to exchange heat from the heat transfer fluid to a water steam mixture in a second circuit. Steam is produced in the second circuit which is injected into the ground formation via the injection well. Produced water from the formation is separated from the extracted oil and recirculated in the second circuit. The first circuit utilizes a clean heat transfer fluid, which may be clean water, to prevent scaling of the solar collection panels. The second circuit uses a relatively dirty water steam mixture. The water returned from the formation includes oil residuals and minerals which would cause scaling of the heat transfer surfaces of the solar collector if this dirty water were directly supplied to the solar field.